Is it really necessary to run swapoff on shutdown?

[Ian Smith]

In freebsd-questions Digest, Vol 585, Issue 5, Message: 21
On Fri, 21 Aug 2015 11:52:04 +0100 Mike Clarke <jmc-freebsd2 at milibyte.co.uk> wrote:
 > I have two 4GB swap partitions on separate drives on my desktop. By
 > the time I shut down at the end of the day I usually have about 8% swap
 > in use.
 > 
 > At an early stage in the shutdown /etc/rc.d/swaplate runs
 > and takes about one minute to run '/sbin/swapoff -aq'. On some occasions
 > when more swap has been used swapoff has failed to complete before
 > timing out.

I guess you could extend the shutdown timeout as a poor workaround?

 > Perhaps I'm misunderstanding the finer details of managing swap space
 > but I would have expected that swapoff could be omitted on shutdown. As
 > each process shuts itself down it will retrieve any swapped out pages
 > which it needs so by the time the last process is finished none of
 > the remaining data in the swap space will be required by anything and
 > can be safely discarded.

Sounds good in theory, but dragons may caution 'shoulds' for 'wills' ..

 > Also if it really is necessary to run swapoff on shutdown should the
 > command have also included the -L option to allow for it having been
 > used in the swapon command.

I know nothing, except noticing that the recent thread 'Swap Questions' 
in -stable@ explores some perhaps related issues, including use of '-L'

http://lists.freebsd.org/pipermail/freebsd-stable/2015-August/083060.html

cheers, Ian